NEET-PG 2015 - Microbiology PYQs Practice Questions

Q: XDR-TB is defined as resistance to which of the following drug combinations?

Fluoroquinolones plus INH plus rifampicin plus amikacin. **Fluoroquinolones plus INH plus rifampicin plus amikacin** - **Extensively drug-resistant tuberculosis (XDR-TB)** is defined by resistance to the most effective anti-TB drugs: **isoniazid (INH)**, **rifampicin**, any **fluoroquinolone**, and at least one of the three injectable second-line drugs (**amikacin**, **kanamycin**, or **capreomycin**). - This combination signifies a substantial therapeutic challenge due to limited treatment options and a high risk of treatment failure. *INH plus rifampicin* - Resistance to **INH** and **rifampicin** defines **multidrug-resistant tuberculosis (MDR-TB)**, which is a precursor to XDR-TB but not XDR-TB itself. - While serious, MDR-TB is not as extensively resistant as XDR-TB, as it doesn't include resistance to fluoroquinolones and second-line injectables. *Fluoroquinolones plus INH plus amikacin* - This combination is incomplete for the definition of XDR-TB because it omits **rifampicin** from the core definition. - XDR-TB specifically requires resistance to both **INH** and **rifampicin** (defining MDR-TB), in addition to resistance to a fluoroquinolone and one of the injectable second-line drugs. *Fluoroquinolones plus rifampicin plus kanamycin* - This combination is also incomplete for the definition of XDR-TB as it omits **isoniazid (INH)**, which is one of the two most crucial first-line drugs that characterize MDR-TB. - XDR-TB builds upon MDR-TB's resistance to both INH and rifampicin. [Practice more Microbiology PYQs on OnCourse]

Q: IFN-gamma is produced by

T-cells. ***T-cells*** - **Interferon-gamma (IFN-γ)** is a crucial cytokine primarily produced by **activated T-lymphocytes**, especially **Th1 cells** and **cytotoxic T lymphocytes (CTLs)**. - Natural killer (NK) cells also produce **IFN-γ**, which plays a key role in **antiviral** and **antitumor immunity**, as well as in promoting **Type 1 immune responses**. *Macrophages* - While macrophages are **responsive to IFN-γ** (e.g., becoming activated), they are not the primary producers of this cytokine. - Macrophages primarily produce other cytokines such as **IL-1, IL-6, TNF-alpha**, and **IL-12** in response to infection or inflammation. *Neutrophils* - **Neutrophils** are key phagocytes in the innate immune system and are primarily involved in engulfing and killing pathogens. - They are not known to be a significant source of **IFN-γ** production; their main defensive mechanisms involve **phagocytosis**, **degranulation**, and **NETosis**. *B-cells* - **B-cells** are central to humoral immunity, specializing in **antibody production** and acting as **antigen-presenting cells**. - They generally do not produce **IFN-γ**; instead, their cytokine repertoire includes **IL-10**, **IL-6**, and **lymphotoxin**. [Practice more Microbiology PYQs on OnCourse]

Q: In the context of immune response, which of the following cell types does not express MHC class II molecules?

NK cells. ***NK cells*** - **Natural Killer (NK) cells)** are innate lymphocytes that do **NOT express MHC class II molecules** under any circumstances. - NK cells use alternative recognition mechanisms (KIRs, activating receptors) to detect target cells, primarily recognizing the **absence of MHC class I** or stress-induced ligands. - They function in innate immunity without antigen presentation capability. - **This is the best answer** as NK cells never express MHC class II, making them distinctly different from professional APCs. *Cortical macrophages* - **Cortical macrophages** in lymphoid organs are professional **antigen-presenting cells (APCs)** that constitutively express **MHC class II molecules**. - They present processed antigens to CD4+ T helper cells, playing a crucial role in initiating adaptive immune responses. *Medullary macrophages* - **Medullary macrophages** are also professional APCs that constitutively express **MHC class II molecules**. - They participate in antigen presentation and immune surveillance within the medullary regions of lymphoid tissues. *Neutrophils* - Neutrophils are granulocytes that **typically do not constitutively express MHC class II molecules** in their resting state. - However, under certain inflammatory conditions with prolonged stimulation (IFN-γ, GM-CSF), neutrophils can be induced to express low levels of MHC class II. - While neutrophils generally lack MHC class II, **NK cells are the more definitive answer** as they never express MHC class II under any physiological or pathological conditions. [Practice more Microbiology PYQs on OnCourse]

Q: Interleukin 2 is produced by

T helper cells 1. ***T helper cells 1*** - **T helper 1 (Th1) cells** are a primary source of **interleukin-2 (IL-2)**, which is crucial for the proliferation and survival of T cells. - IL-2 acts as a **T-cell growth factor**, promoting the expansion of activated T cells, including cytotoxic T lymphocytes. *T helper cells 2* - **T helper 2 (Th2) cells** primarily produce cytokines like **IL-4, IL-5, IL-6, IL-10, and IL-13**, which are involved in humoral immunity and allergic responses. - While Th2 cells are important for immune responses, they are not major producers of IL-2. *Natural killer cells* - **Natural killer (NK) cells** are part of the innate immune system and produce cytokines such as **interferon-gamma (IFN-$\gamma$)** and **tumor necrosis factor-alpha (TNF-$\alpha$)**. - They are not a significant source of IL-2, which is primarily a T-cell derived growth factor. *Basophils* - **Basophils** are granulocytes involved in allergic reactions and anti-parasitic immunity, producing mediators like **histamine** and cytokines such as **IL-4** and **IL-13**. - Basophils do not produce IL-2; their role is distinct in the immune response compared to T cells. [Practice more Microbiology PYQs on OnCourse]

Q: "Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Cl. septicum. ***Cl. septicum*** - *Clostridium septicum* characteristically forms **"Citron bodies"** - boat-shaped or leaf-shaped pleomorphic organisms in exudates - These spindle-shaped, cigar-like forms are a **distinctive morphological feature** of this organism - Associated with **gas gangrene** and spontaneous myonecrosis, particularly in patients with underlying malignancy or neutropenia - The pleomorphic morphology distinguishes it from other clostridial species *Cl. welchii* - *Clostridium perfringens* (formerly *Cl. welchii*) appears as **large, rectangular, "boxcar-shaped" Gram-positive rods** - Does **not** form citron bodies or show the characteristic boat/leaf-shaped pleomorphism - Most common cause of gas gangrene but has different morphological appearance *Cl. edematiens* - *Clostridium oedematiens* (now *Clostridium novyi*) appears as **large, Gram-positive rods** with subterminal spores - Does not form citron bodies - Associated with gas gangrene but lacks the pleomorphic morphology described *Cl. tetani* - *Clostridium tetani* has characteristic **terminal spores** giving a "drumstick" or "tennis racket" appearance - Does not form citron bodies or pleomorphic shapes - Morphologically distinct with its terminal spore appearance [Practice more Microbiology PYQs on OnCourse]

Question 1

XDR-TB is defined as resistance to which of the following drug combinations?

Accepted Answer

Fluoroquinolones plus INH plus rifampicin plus amikacin

Answer

INH plus rifampicin

Answer

Fluoroquinolones plus INH plus amikacin

Answer

Fluoroquinolones plus rifampicin plus kanamycin

Question 2

IFN-gamma is produced by

Accepted Answer

T-cells

Answer

Macrophages

Answer

Neutrophils

Answer

B-cells

Question 3

In the context of immune response, which of the following cell types does not express MHC class II molecules?

Accepted Answer

NK cells

Answer

Cortical macrophages

Answer

Neutrophils

Answer

Medullary macrophages

Question 4

Interleukin 2 is produced by

Accepted Answer

T helper cells 1

Answer

T helper cells 2

Answer

Natural killer cells

Answer

Basophils

Question 5

"Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Accepted Answer

Cl. septicum

Answer

Cl. edematiens

Answer

Cl. tetani

Answer

Cl. welchii

Question 6

The process by which antigen-specific B lymphocytes are selected and activated to proliferate and produce antibodies is called:

Accepted Answer

Clonal selection

Answer

Class switching

Answer

Group switching

Answer

Hybridisation

Question 7

Multiple drug resistance is transferred through -

Accepted Answer

Conjugation

Answer

Transduction

Answer

Transformation

Answer

Mutation

Question 8

Which of the following is an example of the transfer of drug resistance by conjugation?

Accepted Answer

E coli to streptomycin

Answer

Staphylococci to rifampicin

Answer

Pneumococcus to penicillin G

Answer

M tuberculosis to antitubercular drugs

Question 9

Which bacteria can be isolated using crystal violet blood agar?

Accepted Answer

β-hemolytic streptococci

Answer

Corynebacterium diphtheriae

Answer

Staph aureus

Answer

Meningococcus

Question 10

Which medium is most commonly used for antibiotic sensitivity testing?

Accepted Answer

Mueller-Hinton agar

Answer

CLED agar

Answer

Blood agar

Answer

MacConkey agar

NEET-PG 2015 — Microbiology